Thermo-responsive control



Sept. 16, 1958 Filed Aug. 26, 1953 D. T. CAMPBELL 2 Sheets-Sheet 1 RoommERIAOSTAT' l W 23:31 I 20 I I27 79% a2 46 16 I A" I I A 60/ I LmE 76 v46 GT I 10 a? INVENTOR. .DAVJDZ CZIYPEELL ATTOII'NEZ Sept? 1958 D. T.CAMPBELL 2,851,971

THERMO-RESPONSIVE CONTROL.

Filed Aug. 26, 1953 2 Sheets-Sheet 2 IIIWI HIIII H lllllilllllll IN V ENTOR. 0.41/10 7. CQJIPEELL;

United States atent TWO-RESPONSIVE CONTROL David '1. Campbell,Indianapolis, Ind.

Application August 26, 1953, Serial No. 376,641

3 Claims. (Cl. 110-1) The present invention relates to athermofresponsive control, and is concerned primarily with the provisionof a control of the character indicated, specially useful in a systemfor controlling the ignition and operation of a solid fuel, Stoker-fed,burner. Basically, I have provided a thermo-responsive unit including abimetal bar, or its equivalent, which, under conditions of use, isinitially movable under the influence of heat transmitted thereto byconduction, and which is subsequently movable, in the same direction,under the influence of heat transmitted thereto by convection.

It is a primary object of the invention, then, to provide athermo-responsive control including a bimetal bar, or its equivalent, aportion of which rests, under relatively low temperature conditions, incontact with an element having a relatively high coefiicient of heatconduction, the bar being so supported that, upon an increase in itstemperature, the said portion of the bar will move away from, and out ofcontact with, the highly conductive element; and in which said barportion, upon further increase in temperature, will continue to movefarther and farther from said element of high heat conductivity. Afurther object of the invention is to provide a system in which themovable portion of such a bimetallic bar will, upon initial movementunder the influence of heat transmitted thereto by conduction, shift acontrolled element; and, upon further movement in the same directionunder the influence of heat transmitted thereto by convection, willshift another controlled element.

A still further object of the invention is to provide, in a system ofthe character suggested above, an arrangement whereby the shifting ofthe first controlled element will deenergize an ignition device, whilethe shifting of the second controlled element will throw the entiresystem out of operation.

Further objects of the invention will appear as the descriptionproceeds.

To the accomplishment of the above and related objects, my invention maybe embodied in the form illustrated in the accompanying drawings,attention being called to the fact, however, that the drawings areillustrative only, and that change may be made in the specificconstructions illustrated and described, so long as the scope of theappended claims is not violated.

Fig. 1 is a diagrammatic illustration of a solid fuel burner, ignitionand stoker means therefor, and a control system for such ignition andstoker means, embodying my invention;

Fig. 2 is a sectional view, drawn to an enlarged scale, and showing thethermo-responsive control which constitutes a feature of my invention;and

Fig. 3 is an end elevation of the unit of Fig. 2, viewed from the left.

In Fig. 1, I have diagrammatically illustrated a solid fuel burner suchas a household furnace, indicated by the reference numeral and formed toprovide a combustion chamber 11. A stoker mechanism, indicated geniceerally by the reference numeral 12, is suggested diagrammatically andincludes a driving motor 13. Within the combustion chamber, I haveindicated an electric ignition unit 14, but it will be understood thatany kind of ignition unit may be used in the present system, so long asit is capable of being activated electrically.

At 15, I have indicated the conventional smoke pipe or stack, leading toa chimney 16; and at 17, I have indicated a conventional roomthermostat. The illustrated system is a high voltage system, usinghousehold circuits; but it will be clear that my invention isapplicable, also, to systems in which the control circuits aresecondary, low-voltage circuits.

The two sides of a household current supply are indicated at 18 and 19.The line 18 is connected to the stationary contact 21) of the roomthermostat 17, while a movable contact 21 thereof is conventionallysupported upon a bimetallic, thermo-responsive bar 22. A wire 23connects said contact 21 with one contact 24 of a limit switch,indicated generally by the reference numeral 25. The other contact 26 ofthe switch is connected by a wire 27 with the movable element 28 of adouble-contact switch indicated generally by the reference numeral 29.The switch 29 is so constructed and arranged that, under normalconditions, the contact 28 engages a contact 30 thereof, said contact 23being movable, under conditions later to be described, out of engagementwith the contact 30 and into engagement with the contact 31.

A wire 32 leads from the contact 28 of the switch 29 to a movablecontact 33 of a switch indicated generally by the reference numeral 34.The stationary contact 35 of the switch 34 is connected, by wire 36,with one terminal of a motor 37, the other terminal of which isconnected by wire 38, with the line wire 19.

A wire 39 connects wire 32 with the movable contact 40 of a furtherswitch 41, the stationary contact 42 of which is connected, by wire 43and a wire 44, with one terminal of the motor 13, the other terminal ofwhich is connected to line wire 19. A wire 45 connects wires 43 and 44with the contact 31 of switch 29.

A wire 46 leads from contact 31 of switch 29 to the wire as; and a wire47 connects said wire 4-6 with the stationary contact 48 of a furtherswitch 49, the movable contact 54) of which is connected, by wire 51,with one end of the igniter unit 14, the other end of said unit beingconnected, by wire 52, with line wire 19.

Motor 37 drives a triple cam wheel comprising cam surfaces 53, $4 and55. The movable contact 33 of the switch 34 carries a finger 56 whichrides the cam surface 53; the movable contact 4t) of switch 41 carries afinger 57 which rides the cam surface 534; and the movable contact 5d ofthe switch 49 carries a finger 58 which rides the cam surface 55.

Fig. 1 illustrates the rest positions of the parts of the controlsystem. When the room thermostat 17 calls for heat, a circuit energizingthe motor 37 is established from line wire 18 through thermostat contact2 contact 21, wire 23, contact 2% of switch 25, contact 26, wire 27,contact 28, contact 31 wire 46, wire 36, motor 37, wire 38, and linewire 19. The motor 3'7 is thus energized to drive the cam wheel in aclockwise direction. The system is so proportioned and designed that themotor 37 will drive the cam wheel through one revolution in twentyminutes. During the first minute of such operation, the finger 56 ridesthe node of the cam surface 53, the finger 58 rides the node of the camsurface 55, and the finger 57 rides the node of the cam surface 54, sothat all of the switches remain in their illustrated conditions. If,during this period, the contact 28 of the switch 29 should be moved outof engagement with the contact 31), or if the contact 26 of the switch25 should be moved out of 3 engagement with the contact 24, the motor 37will be stopped.

However, if the elements of the control unit 59 remain in theirillustrated positions, after one minute of operation ofrthe motor 37,the fingers 56 and 58 will simultaneously drop off the nodes of theirrespective cams, thus closing switches 34 and 49. Closure of the switch34 establishes a holding circuit for energizing the motor 37, which istraced from line wire 18 through contacts 20 and 21 of the thermostat17, wire 23, contact 24, contact 26, Wire 27, wire 32, movable contact33 of switch 34, contact 35, Wire 36, motor 37, and wire 38 to line wire19. It will be seen that this circuit is independent of the contacts 28and 30 of switch 29, so that, though the contact 28 may be moved out ofengagement with contact 30, the motor 37 will continue to run, onceswitch 34 has been closed, until that switch is reopened as the finger56 rides onto the node of its cam 53 after completion of one full'rotation of that cam.

Closure of the switch 49 establishes an energizing circuit for theignition unit 14, which is traced from line wire 18 through the contacts20 and 21 of the room thermostat 17, wire 23, contact 24, contact 26,wire 27, contact 28, contact 30,. wire 46, wire 47, contact 48, contact50, wire 51, ignition unit 14, and wire 52 to line wire 19. Thus, solong as contacts 24 and 26 remain in engagement, and contacts 28 and 30remain in engagement, and switch 49 remains closed, the ignition unit 14will remain energized.

The cam wheel is so proportioned and designed that the switch 49 willremain closed for five minutes. At the end of that time, the finger 58rides onto the node of the cam 55 and, substantially simultaneously, thefinger 57 drops oil the node of the cam 54. Thus, the switch 49 isopened and substantially simultaneously the switch 41 is closed. Thus,the ignition unit 14 is deenergized and an energizing circuit for themotor 13 of the stoker 12 is established, traceable from line wire 18through contacts 20 and 21 of the thermostat 17, wire 23, contact 24,contact 26, wire 27, wire 32, wire 39, contact 40, contact 42, wire 43,Wire 44, motor 13 and line wire 19.

The cam wheel is so proportioned and designed that these conditions, inwhich switch 34 and switch 41 are closed and switch 49 is open, willcontinue for a further period of fourteen minutes to complete thetwentyminute cycle of the cam wheel driven by the motor 37. Ordinarily,combustion within the chamber 11 will take place during this period offourteen minutes, preceded by the ignition period of five minutes; and,if combustion does occur, the temperature of the smoke pipe or stack 15will be raised sufiiciently to cause the contact 28, under the influenceof the control later to be described in detail, to shift out ofengagement with the contact 30 and into engagement with the contact 31.

It will be noted that such shifting of the contact 28 will not aflecteither the holding circuit for the motor 37, which extends through theswitch 34, or the above-traced energizing circuit for the motor 13,which extends through the switch 41, both of these circuits beingindependent of the contacts 28 and 30. However, when the switch 34opens, under these conditions, the motor 37 will be deenergized, sincethe primary circuit therefor does extend through the contacts 28 and 30.

Movement of the contact 28 into engagement with the contact 31establishes an energizing circuit for the motor 13, independent of theswitch 41. That circuit may be traced from line wire 18 through contacts20 and 21 of thermostat 17, wire 23, contact 24, contact 26, wire 27,contact 28, contact 31, wire 45, wire 44, motor 13, and line wire 19.Thus, once combustion has been established, the motor 13 will continuein operation for as long 'as the thermostat 17 calls for heat, unlessthe switch 25 opens, or the contact 28 moves out of engagement with thecontact 31. As will appear from the following description, the switch 25will be opened only if the temperature of the smoke pipe 15 exceeds apredetermined maximum, while the contact 28 will move away from thecontact 31 only if the temperature of the stack 15 drops below apredetermined minimum. Thus it will be seen that the switch 29constitutes a doublecontact switch having a normal position (asillustrated) for permitting closure of the igniter energizing circuitwhile temporarily preventing closure of the fuel supplying circuit, andhaving an abnormal position (with contacts 28 and 3t) engaged) closingsaid fuel supplying circuit while preventing closure of said ignitercircuit.

Referring now to Figs. 2 and 3, it will be seen that the unit 59comprises a housing 69 within which the switches 25 and 29 are enclosed.Terminals or binding posts 77, 78, 79 and provide for convenientlyconnecting the leads to and from the switches 25 and 29 with the severalwires 23, 32, 45 and 46, as will appear hereinafter.

The housing 60 is formed to provide a base or floor 63 having lateralflanges 64, 64, for protecting a plate 61 of copper or other suitablematerial having a high coeflicient of heat conductivity. A sheet of heatinsulating material, such as asbestos, or the like, overlies the innersurface of the plate 61, and is indicated by the reference numeral 62.The insulating sheet 62 and the floor 63 are perforated or apertured at65 and 64, respectively, to expose a section 66 of suitable length, ofthe inner surface of the plate 61, to the interior of the housing 60.

A bracket 67 is suitably supported within the housing 60, and one end 68of a bimetallic bar, indicated generally.

by the reference numeral 69, is suitably anchored upon the bracket 67.The bar 69 is bent or folded, as at 70, so that its opposite end 71 liesat a substantial angle to the position of the end 68 thereof. The partsare so proportioned and designed that, when the temperature of the bar69 is below a predetermined minimum, the end portion 71 of said bar willlie in intimate contact with the exposed portion 66 of the inner surfaceof the heatconductive plate 61, so that heat may be transmitted to theend portion 71 of the bar 69 by direct conduction through the plate 61.The bar 69 is so arranged that an increase in the temperature impressedthereupon causes the end portion 71 thereof to move upwardly, as viewedin Fig. 2, thus moving away from the surface 66 of the plate 61.Obviously, initial movement of the bar end portion 71, under theinfluence of an increase in its temperature above the predeterminedminimum, shifts said bar end portion out of contact with the plate 61,so that the transfer of any further heat to said bar end portion,further to increase its temperature, must be. by convection through theair enclosed within the housing 60.

As a consequence of this arrangement, the bar is, of course, highlysensitive to heat supplied to the plate 61 at all temperatures up to andincluding the above-mentioned predetermined minimum, but is much lesssensitive to heat supplied to said plate, at temperatures above thepredetermined minimum, after the bar end portion 71 has moved out ofcontact with the plate 61.

The switch 29 is provided With an actuator arm 72 which carries, at itsouter end, a roller 73 resting upon the upper surface of the bar endportion 71, and yieldably held in engagement with the bar and in anysuitable manner. As illustrated, the switch 29 is a conventional,double-contact, micro-switch, provided with the usual operating button74, spring pressed outwardly; and said button bears against the actuatorarm 72 to hold the roller 73 resiliently in engagement with the bar endportion 71. The parts are so arranged, of course, that when the arm 72is in its illustrated position, the contact 28 is in engagement with thecontact 30; but initial movement of the bar end portion 71 out ofcontact with the plate 61 will shift the roller 73, and so the arm 72,sufficiently to shift the contact 28 out of engagement with the contact30 and into engagement with the contact 31.

The switch 25 is provided with an actuating plunger 75, disposed in thepath of the movable end of the arm 72. Under normal conditions, and withthe plunger 75 in its illustrated position, the contact 26 will be inengagement with the contact 24; but when the plunger 75 is movedupwardly, as the bar end portion 71 moves to its dotted line position,the movement of the plunger 75 will shift the contact 26 out ofengagement with the contact 24.

The base 63, insulating sheet 62 and plate 61 are formed with aplurality of apertures 81 therethrough, for the reception of screws 82,or the like, whereby the unit 59 may be secured to the smoke pipe orstack 15, in the manner suggested in Fig. 3, with the plate 61 inintimate contact or engagement with the outer surface of the metallicsmoke pipe. Preferably, one side of the housing 60 will be open, andwill be normally closed by a cover 83, suitably secured in place byscrews 84, or the like.

It will now be obvious that, when combustion does not exist within thechamber 11, so that the smoke pipe 15 is relatively cold, the controlparts will be in the positions illustrated in Fig. l, and the bimetallicbar 69 will be in its condition illustrated in solid lines in Fig. 2. Ifthe thermostat 17 calls for heat, the motor 37 will be energized, in themanner described above, to carry the control system through the cyclewhich has been described in detail. If combustion within the chamber 11is successfully initiated, the smoke pipe will be quickly warmed, andheat will be transmitted therefrom through its metal wall, through thecopper plate 61 and to the bimetallic bar end portion 71 which will bequickly affected to flex out of engagement with the exposed surface 66of the plate 61. Such flexure of the bar will shift the actuator 72 ofthe switch 29 to disengage the contact 28 from the contact 30 and moveit into engagement with the contact 31. Preferably, the switch 2 will beso constructed as to provide for snap action of the contact 28.

Fluctuations in the temperature of the smoke pipe, between theabove-mentioned minimum and a predetermined maximum, will causerelatively slight, and rather sluggish, movements of the end portion 71of the bar 69; and said end portion will not move far enough, undernormal conditions, to cause the plunger 75 of the switch 25 to beshifted. However, if for any reason the temperature within the smokepipe should rise to a dangerous value, the bar end portion 71 will becaused to move far enough to shift the plunger 75, thereby opening thelimit switch 25 in the manner above described.

It will be clear, of course, that so long as combustion exists withinthe chamber 11, at a temperature suflicient to permit normal operationof the stoker, a call for heat through the thermostat 17 will notenergize the motor 37 and will not energize the igniter unit 14, sincethe primary circuit for the motor 37 must go through the contacts 28 and30, and since the igniter unit 14 can be energized only through theswitch 49 which is open at all times except when the finger 58 is ridingthe lower portion of the cam surface 55. So long as the contact 28 is inengagement with the contact 31, a call for heat through the thermostat17 merely energizes the motor 13 without affecting any other portions ofthe control.

While the unit 59, including the bimetallic bar 69 having its endportion 71 normally in direct engagement with the plate 61 of high heatconductivity, finds its primary utility in the system illustrated inFig. 1, it will be clear that such a unit will be useful, also, in othersystems. I presently believe that I am the first to have conceived theidea of providing a thermo-responsive element so constructed andarranged that, within a relatively low temperature range, it is subjectto temperature variations transmitted thereto by conduction, while, in arelatively high temperature range, it is subject to temperaturevariations transmitted thereto only by convection.

I claim as my invention:

1. A thermo-responsive unit comprising a bi-metallic 6 element, ahousing enclosing said element, a member subject to temperature changesand having a portion whose outer surface is exposed to such temperaturechanges and whose inner surface is exposed to the interior of saidhousing, means in said housing supporting said bi-rnetallic element insuch a position that, when said element is relatively cool, a portiononly of said element lies in contact with said inner exposed surface ofsaid member, fiexure of said element in response to elevation of thetemperature thereof acting to move all of said element portion out ofcontact with said inner exposed surface of said member, a firstshiftable member disposed in said housing in the path of said elementportion and actuable thereby upon movement of said element portion outof such contact, and a second shiftable member disposed in said housingin the path of said element portion and actuable thereby upon furthermovement of said element portion under the influence of heat transmittedthereto from said first named member solely by convection.

2. A thermo-responsive switch unit comprising a housing having a wallformed of material of relatively high heat conductivity, a firstelectric switch and a second electric switch mounted within saidhousing, a bi-metal bar, means within said housing supporting one endportion of said bar, the other end portion of said bar being disposed ata substantial angle to said one end portion and lying, when said bar isrelatively cool, flatly in contact with an exposed internal portion ofsaid wall, fiexure of said bar in response to elevation of thetemperature thereof acting to shift said other end portion thereoftoward said one end portion thereof and out of contact with said exposedwall portion, an actuator for one of said switches disposed in the pathof said other bar end portion to be shifted thereby, as said other barend portion leaves contact with said exposed Wall portion under theinfluence of heat transmitted thereto by conduction, and an actuator forthe other of said switches disposed for shifting in response to furthermovement of said other bar end portion under the influence of heattransmitted thereto by conviction through the atmosphere within saidhousing.

3. In a control system for a burner including a combustion chamber, anelectrically-activated i nitcr, electrically-activated means forsupplying fuel to said combustion chamber, and a stack for conductingcombustion products from said chamber, an energizing circuit for saidigniter, an energizing circuit for said fuel supplying means, adouble-contact switch having a normal position for permitting closure ofsaid igniter energizing circuit while temporarily preventing closure ofsaid fuel supplying circuit and an abnormal position for closing saidfuel supplying circuit while preventing closure of said igniter circuit,and a normally closed limit switch dominating both of said circuits, theinvention which comprises a housing having a wall formed of material ofrelatively high heat conductivity, means securing said housing to saidstack with the external surface of said housing wall in intimateheat-conducting contact with said stack, a bi-metal bar, means withinsaid housing supporting one end portion of said bar, the other endportion of said bar being disposed at a substantial angle to said oneend portion and lying, when said bar is relatively cool, flatly inheat-conducting contact with the internal surface of said housing wall,fiexure of said bar in response to elevation of the temperature thereofacting to shift said other end portion of said bar toward said one endportion thereof and out of contact with, and away from, said housingwall, an actuator for said double-contact switch disposed closely in thepath of said other end portion of said bar to be shifted thereby, uponinitial movement of said other end portion out of contact with saidhousing Wall, whereby said double-contact switch is actuated to itsabnormal position, and actuating means for said limit 7 switchcomprising an actuator disposed for actuation, by movement of said otherend portion of :said bar to a substantial degree away from said housingWall, to open said limit switch.

References Cited in the file of this patent UNITED STATES PATENTS2,008,163 Walder July 16, 1935 8 Dezotell July 13, 1937 Varley Dec. 27,1938 Scoggin et al Apr. 1, 1941 Sahli Sept. 30, 1941 Scott et a1 Apr.21, 1942 Eldredge July 14, 1942 Hotchkiss Oct.2,' 1945 Patent No,2,851,971

September 16, 1.958

David To Campbell It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionand that the said Letters Patent should read as corrected below.

Column 6, lines 19 and 20, strike out "by convection and insert insteadthrough the ambient atmosphere Within said housing line 41, for"conviction" read conveetion Signedand sealed this 18th day of NovemberU958,

(SEAL) Attest:

KARL H o AXLINE Attesting Ofi'icer ROBERT C. WATSQN Commissioner ofPatents UNITED STATES PATENT OFFKCE CERTlFICATE 0F QQRMTHUN Patent No.2,851,971 September 1.6 1958 David "T, Campbell It is hereby certifiedthat error appears in the printed specification of the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below.

Column 6, lines 19 and 20, strike out "by convection" and insert insteadthrough the ambient atmosphere within said housing line 41, forconvieiiorr read convection Signedvand sealed this 18th day of November1958.,

(SEAL) Attest:

KARL AXLINE 7 ROBERT C. WATSQN Attesting Oflicer Commissioner of Patents

